UW Professor Determines Prehistoric Stone Objects May Have Served as Hunting Weapons

Prehistoric stone objects, once thought to be used only as tools to shape and grind other materials or process food, are now receiving further analysis: as potential projectile weapons used for hunting to injure or kill large mammals.

These ball-shaped objects, known as spheroids, could be used to inflict significant damage on prehistoric mammals at distances up to 25 meters, says Qin Zhu, an associate professor in the University of Wyoming’s Division of Kinesiology and Health. His research focuses on motor learning and control, and human perception and action.

Zhu is co-author of a paper, titled “A Dynamic Analysis of the Suitability of Prehistoric Spheroids from the Cave of Hearths as Throw Projectiles,” that was recently published in Scientific Reports. Scientific Reports is an online, open access journal from the publishers of Nature. The journal publishes scientifically valid primary research from all areas of the natural and clinical sciences.

“We were being selective,” Zhu says of the spheroid number (55) used in the research. “For our simulation or calculation to work, we had to make sure all of the spheroids were round to meet our criteria. About 81 percent of the spheroids, if thrown properly, had the ability to inflict pain or damage to a medium-sized animal like an impala antelope.”

This paper applies research on how modern humans perceive the throwing affordances of objects to inform a mathematical analysis of spheroids used to evaluate the potential of these objects as projectiles for throwing. The paper describes these 55 spheroids, and then outlines the approach to affordance perception that informs current research into how perception-action systems select and control skilled behaviors.

Spheroids are found in the Middle Pleistocene site of Cave of Hearths in the Makapana Valley in South Africa, in levels dating from 1.8 million years ago (Early Stone Age) to at least 70,000 years ago (Middle Stone Age), making them one of the oldest and longest-used technologies.

The goal of the simulations was to evaluate the amount of damage these objects could achieve if thrown by ancient humans. While other animals have been known to throw objects on occasion, none can match the speed, accuracy and distances that trained humans can achieve, the paper says.

A popular hypothesis made by archaeologists is that spheroids were used to make stone tools; as grinding stones for processing plant material; to break bones; as tools to re-sharpen grinding slabs; and as bolas stones for hunting.

Before throwing spears were developed, humans were faced with finding and using objects suitable for hunting and self-defense. The ability to hurt or kill prey from a distance expanded the range of a human’s food source while simultaneously reducing close confrontations with dangerous prey, the paper says.

“They did actually find bones of animals in the cave,” Zhu says of the South African site.

This Scientific Reports paper utilized data from two papers Zhu previously had published. One, which appeared in Human Movement Science in 2009, discovered the functional relationship between release velocity and the weight of a throwing object so that the former can be predicted by the latter. The other, published in Evolution and Human Behavior in 2011, showed how the robust size-weight illusion in perceiving an object’s weight actually serves to detect the best object for throwing, which has relevance to human evolution. The part of the brain -- the cerebellum -- that is responsible for coordination in performing complicated motor skills, like over-arm throwing, is the same part of the brain used to develop language, Zhu says.

Andrew D. Wilson, from Leeds Beckett University in Leeds, United Kingdom, was the paper’s lead author. Lawrence Barham and Ian Stanistreet, both from the University of Liverpool in Liverpool, England; and Geoffrey Bingham, of Indiana University, also contributed.

Zhu says the study may be extended to take into account other different-shaped spheroids or different-sized animals.